Intelligent STEP-NC controller

ABSTRACT

An intelligent STEP-NC (Standard for the Exchange of Produce model-Numerical Controller) overcomes short-comings of conventional NCs with a closed structure The intelligent STEP-NC intelligently performs a machining process based on ISO 14649 data while autonomously coping with an emergency at a shop-floor. Thus, the discontinuity of information in a CAD-CAM-CNC chain where the current NCs are operated can be overcome and the concept of “design-to-manufacture” can be realized.

FIELD OF THE INVENTION

The present invention relates to an intelligent STEP-NC (Standard forthe Exchange of Product model-Numerical Controller) controller.

BACKGROUND OF THE INVENTION

Some among various techniques for modularizing a NC (numericalcontroller) are OSACA (Open System Architecture for Controls withinAutomation systems) in Europe, OMAC (Open Module Architecture Controls)in U.S., OSEC (Open System Environment for Controllers) in Japan, etc.Prior arts concerned with these techniques are introduced in a paperdirected to a holonic NC based on a holonic manufacturing paradigm(Kurth 1994, Suh et al. 1998); to a TRUE-CNC serving as a NC systemhaving a CAD, a CAPP, a CAM, a CNC (Computer-based Numerical Control), amonitoring and a verifying function (Yamajaki et at. 1997); and to aproduction cell based on a programming interface (Brouer et al. 1997),etc. These conventional techniques are developed to overcome a closedstructure of prior NCs. However, they do not specify therein a moduleand its structure for realizing an intelligent NC controller.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide an intelligentSTEP-NC (Standard for the Exchange of Product model-NumericalController) capable of performing a machining process based on an ISO14649 data model while effectively coping with an emergency at ashop-floor, thereby overcoming discontinuity of information in aCAD-CAM-CNC chain and realizing a “design-to-manufacture” concept in thetrue sense.

In accordance with the present invention, there is provided anintelligent STEP-NC including a control module for reflecting functionallevel requirements of each controller of a machining tool; a SFP/TPGmodule for reflecting data interface level requirements; and a common DBmodule for storing therein data generated, updated and referred to bythe control module and the SFP/TPG module.

The present invention describes a method for designing and operating acontroller based on an analysis of problems or requirements in afunctional aspect and a data interface as well as an implementationalaspect at a shop-floor.

The most important function of the CNC is to control a machining processto precisely machine a targeted feature by a cutting process. The maininterest of the intelligent STEP-NC resides in accomplishing a machininggoal by effectively coping with varying conditions at the shop floor.The present invention pursues the realization of such an intelligentSTEP-NC by considering self-operated functions, interactions with anoperator, an error recovery, a quality control, a resource management,learning, and cooperative functions.

Software elements constituting the intelligent STEP-NC controller areself-operated without a detailed direction from the operator. Further,in order to minimize directions from the operator and interactionsbetween the operator and the controller, the operator's interference inthe controller is minimized and tasks allotted to the operator areclearly distinguished from those allotted to the controller. Theintelligent STEP-NC controller is capable of handling unexpected errorsor changes occurring during a machining process. As for the qualitycontrol, an OMM (on-machine measurement) is performed and a properdiagnosis is provided in order to minimize geometric errors betweendesigning features and machining features. For the sake of an optimummachining of a targeted feature, cutting parameters are set to bevariable depending on machining conditions rather than fixed. In thematter of the resource management, all the resources included in themachining process are managed and controlled. The intelligent STEP-NC iscapable of performing a high-speed machining process withoutdeteriorating a luminous intensity of a surface of a machined feature.Further, the intelligent STEP-NC can acquire machining knowledge and addthe acquired knowledge to a knowledge base so as to improve theperformance efficiency of the controller.

The technical essence of the intelligent STEP-NC controller lies inovercoming a shortcoming of a G-code input in a conventional NC andimproving a limited data processing efficiency of the conventional NC.That is, the key technology of the intelligent STEP-NC controllerrelates to a data interface between the CAM and the CNC and, also, to adata processing within the CNC. To achieve the above technical goal ofthe intelligent STEP-NC controller, the present invention considers astandard schema, a CAD data interface, an Internet interface, a processplanning, a tool-path generation and a machining simulation. In theintelligent STEP-NC controller, the controller directly receives a CADdata so as to utilize geometric information which is lost in theCAD-CAM-CNC connection. Reflected in implementing an interface betweenthe CAM and the CNC are an ISO 10303 data model serving as aninternational standard in a manufacturing field for expressing acomponent model, an ISO 13399 for defining cutting tools and an ISO14649 data model serving as a NC data standard. Control software of theintelligent STEP-NC controller performs a remote control through theInternet and provides a function of monitoring the controller. In case apart program generated by the CAD/CAM system is modified at theshop-floor, problems may occur due to the inconsistency of the data. Inorder to avoid such problems, the intelligent STEP-NC controller enablesa bi-directional data communication between the CAM and the CNC. Theintelligent STEP-NC controller establishes a process plan and generatesa tool-path on the basis of the prepared process plan. The controllerfor autonomously generating the tool-path may have a feature-baseddesign data as an input thereto. Before the actual machining process,the intelligent STEP-NC controller simulates the machining process tofind a possible error and verify the tool-path.

The intelligent STEP-NC controller is an open type controller having asoftware-based structure, which can be customized by the operator. Allcontrol modules, except an interface board for connecting the controllerto hardware (a driver, a motor and a machining tool), in an operatingsystem widely employed on a PC platform are implemented on a softwarebasis. Further, since the controller is designed to have the open typearchitecture, the operator can access and modify the internal functionsof the controller. Furthermore, since the intelligent STEP-NC uses asoftware-based module structure design, the operator can readilyrestructure the modules of the controller, in which case the wholeprogram of the controller need not be recompiled and each module isoperated on a plug-and-play basis.

BRIEF DESCRIPTION OF THE INVENTION

The above and other objects and features of the invention will becomeapparent from the following description of preferred embodiments givenin conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of an intelligent STEP-NC controller inaccordance with a preferred embodiment of the present invention;

FIGS. 2A and 2B describe a process for operating an intelligent STEP-NCcontroller in accordance with the present invention;

FIGS. 3A and 3B illustrates a process for developing an intelligentSTEP-NC controller in accordance with the present invention; and

FIGS. 4A to 4C offer a data model for a measurement, a monitoring and anadaptive control in an intelligent STEP-NC controller in accordance withthe present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring to FIG. 1, there is provided a block diagram of an intelligentSTEP-NC controller in accordance with a first embodiment of the presentinvention. The intelligent STEP-NC controller includes a SFP (shop-floorprogramming)/TPG (tool-path generation) module 10, a common databasemodule 12 and a control module 14.

The control module 14 reflects functional-level requirements of each ofcontrollers of a machining tool, wherein the controllers constitute themachining tool based on a holonic paradigm including a decision-making,an execution and a monitoring stage.

The control modules 14 includes a decision maker for managing anintra-task, an executor, a monitor, an emergency handler, a plurality ofmodules for supporting non-machining functions such as a NCK/PLC(Numerical Control Kernel/Programmable Logic controller), a communicatorfor managing an inter-task, an inspector, a learner and a setup manager.

The setup manager within the control module 14 supports a setup of aworkpiece. Once the workpiece is placed on the machining tool, the setupmanager moves a touch probe by using geometric information of theworkpiece and a jig to find a setup reference position.

The decision maker determines a working sequence based on a diagnosisresult provided from the emergency handler, a monitoring result receivedfrom the monitor and an inspection result sent from the inspector. Thedecision maker selects the next process among various alternative plansof a non-linear type. The non-linear process plan includes a selectiveprocess plan and can be expressed by an “AND-OR” graph. It is one of themost important tasks of the decision maker to set priority between aplanned process and a process demanded by the emergency handler.

The executor converts a task provided from the decision maker into acommand and transfers the converted command to the NCK/PLC. If the taskis concerned with a machining process, the executor brings the NCK/PLC acorresponding tool-path from a tool-path database (DB) within the commonDB modules 12. If the task is directed to a tool exchanging process, onthe other hand, the executor searches a tool magazine to find analternative tool and, then, provides the found alternative tool to theNCK/PLC. Further, the executor stores therein a command performed by theNCK/PLC for an adaptive control. FIG. 4C illustrates a data model forthe adaptive control.

The NCK/PLC modules are for directly operating the machining tool. TheNCK interprets a tool-path command provided from the executor andperforms the command by driving a servo-mechanism. The PLC performs amachining tool command concerned with, e.g., a tool exchange and aloading/unloading of the workpiece. Further, for the sake of a free formcurve machining, the NCK supports NURBS interpolation to thereby realizea high-speed machining of the workpiece by using a small amount of data.

The monitor continuously monitors the whole machining status by usinginformation from sensor signals and, then, provides the monitoringresult to the emergency handler or the decision maker. FIG. 4Billustrates a data model for monitoring. A tool-monitoring and anemergency detection are key functions of the monitor.

If an emergent situation is reported by the monitor, the emergencyhandler diagnoses the emergency to determine how to handle theemergency. The diagnosis result is delivered to the decision maker,which is in charge of making a final decision and scheduling. Forexample, if the emergency is related to a damage of a tool, theemergency handler retreats the damaged tool and checks whether thereexists an alternative tool in the tool magazine by using the machiningresource DB. If the alternative tool is found, the machining process isresumed by using the found alternative tool. If the alternative tool isnot found, however, the emergency handler notifies the decision maker ofsuch a result and waits for a final decision of the decision maker. Ascan be seen from the above description, the emergency handler may beconsidered as a special type of decision maker for only dealing with anemergent situation.

The inspector automatically performs both an in-process inspection and apost-process inspection on the machining tool by using an OMM(on-machine measurement) and provides the inspection results to thedecision maker. The in-process inspection result is delivered to thelearner as well. FIG. 4A illustrates a data module for the OMM. Theinspector generates a tool-path for the touch probe and stores thetool-path data in an inspection DB. The inspector also calculates ageometric error between a design feature and a corresponding machiningfeature by comparing the inspection DB and a machining feature DB.

The learner analyzes the in-process information obtained from theinspector by using an expert algorithm and, then, stores the analyzedinformation in a machining knowledge DB.

The communicator interacts with external units such as the CAD/CAMsystem, a shop-floor control system and an operator. If the CAD/CAMsystem raises a request, a controller transmits to the CAD/CAM system apart program stored in a current controller DB. If the shop-floorcontrol system sends a request, the controller makes a report onmachining status and problems that occurred during the machiningprocess. Further, if it becomes impossible to process a certain taskbecause of an unexpected problem, the communicator notifies the operatorof the problem.

The SFP/TPG module 10 reflects data interface level requirements of thecontroller. The SFP/TPG module 10 incorporates a function of a CAM intoa SFP system based on the STEP-NC data model.

The SFP/TPG module 10 includes an input manager, a process planner, atool-path generator and a simulator.

The input manager within the SFP/TPG module 10 converts a standard CADdata (STEP AP203) into an internal feature modeling kernel data,recognizes a machining feature, extracts a property value of themachining feature and stores the extracted property value in themachining feature DB in the common DB modules 12.

The process planner receives from the input manager the property valueof the machining feature and determines a process sequence, a machiningtask, a jig, a setup and a cutter that are required for themanufacturing of the machining feature. Thus determined information isstored in the machining process DB. The process sequence is expressed asone of nonlinear process plans and the decision maker selects a properone among the nonlinear process plans during the machining process. Anoptimum cutting parameter, a machining strategy and the cutter isdetermined by using the machining knowledge DB. To this end, aknowledge-based process planning system is required.

The tool-path generator receives from the process planner the planneddata. Then, the tool-path generator generates a tool-path for machiningand measurement, and stores the generated tool-path in a tool-path DB.The generated tool-path is a complete one including connection pathsbetween an approach path, a retract path, a machining path and ameasurement path. The tool-path is stored in the tool-path DB which isaccessible by the NCK/PLC. Since the NCK/PLC can interpret a NURBScurve, the tool-path generator need not divide the tool-path for freeform curves into segments or arcs.

The simulator receives the generated tool-path from the tool-pathgenerator and performs a cutting simulation before an actual machiningprocess starts in order to verify the generated tool-path and findpossible errors therein. The simulator detects through the cuttingsimulation an under-cut or an over-cut of a feature and a toolinterference. In addition to the error detection, the simulatorcalculates an optimal cutting rate by using a workpiece removal rateduring a solid cutting simulation. The simulation results are stored inthe tool-path DB and the machining process DB.

The common DB modules 12 store therein the data generated, updated andreferred to by the control modules 14 and the SFP/TPG modules 10.

The common DB modules 12 include the machining feature DB, the machineresource DB, the machining process DB, the machining knowledge DB, thetool-path DB and the inspection DB. The machining feature DB, thetool-path DB and the inspection DB are short-term databases while themachine resource DB and the machining knowledge DB are long-termdatabases. When a part machining is completed, the short-term databasesare removed.

The machining feature DB within the common DB modules stores therein themachining feature information generated by the input manager. The storeddata serves as a feature-based input for the process planner.

The machine resource DB stores therein information upon a structure of amachine, available tools, a tool magazine, a jig and a sensor. Themachine resource DB is updated by the operator or the decision maker.

The machining process DB store therein a nonlinear process plangenerated by the process planner. The machining process is expressed byusing the machining features, the machining operations, the machiningstrategy, the cutting parameter and the tools.

The machining knowledge DB interacts with the expert system to storetherein long-term machining knowledge for use in the process planner andthe executor. The machining knowledge DB is updated by the learner.

The tool-path DB stores therein the tool-path generated by the tool-pathgenerator. The tool-path DB can be accessed by the NCK/PLC and thesimulator.

The inspection DB stores therein the tool-path for the measurement aswell as the result measured by the inspector.

Referring to FIGS. 2A and 2B, there is described a process for operatingthe intelligent STEP-NC in accordance with the present invention. Theintelligent STEP-NC controller is not completely automated but operatedby interactions with the operator. The STEP-NC operational process isdivided into two stages, a part programming stage and a CNC operationstage.

A feature designer designs a feature to be manufactured by employing aCAD system that supports an AP203 data model. The designed feature isprovided to a process designer. That is, the designed feature data isdelivered to an off-line CAM system, i.e., an external SFP system or aSFP system installed within the intelligent STEP-NC.

In the SFP system, the input manager recognizes machining features basedon the AP203 file inputted thereto. The recognized machining featuresare stored in the machining feature DB.

The process planner sets up a machining operation for each of themachining features and, then, determines a machining method, a machiningstrategy, a cutter and a cutting parameter for each of the machiningoperation. These process plans are based on ISO 14649 data model.

Based on the recognized machining features, the user sets the sequenceof workingsteps. The cutting parameter is determined on the basis of areference value recommended by the knowledge-based system and, ifrequired, an adaptive control mode is set up.

However, a tool-path for each of the workingsteps is not defined becausethe tool-paths are to be generated by an intelligent CNC. The userspecifies an inspection task on a PSG (process sequence graph) whichdisplays the process plan.

If an input is provided from the user, the SFP system automaticallycreates an ISO 14649 part program.

However, in case the built-in SFP system is employed, it becomesunnecessary to produce the part program because all necessary inputinformation is stored in the DBs of the controller. Further, in case theinput from the user is not the STEP AP type CAD data but an ISO 14649part program, the input is downloaded to the intelligent STEP-NC throughthe Internet or a DNC.

The intelligent STEP-NC interprets the ISO 14649 part program and storesthe interpreted information in a corresponding DB. If the part programis produced by a built-in SFP prepared in the controller, theinterpretation of the part program becomes unnecessary.

The tool-path generator of the controller generates a tool-path for acutter and a touch probe, respectively, and the generated tool-paths arevisualized and verified by the simulator. Then, the calculatedtool-paths are utilized as a reference tool-path for the machiningoperations. Although the tool-paths are preferably generated before themachining operations, it is also possible to create the tool-pathsduring the machining operation in an emergency situation caused by,e.g., a broken or worn-out tool.

By pushing a start button after a workpiece is loaded, the machiningoperation starts. First, a setup manager automatically searches for areference position by using the touch probe. Then, the decision makerselects the next workingstep according to the PSG that represents thenon-linear process plan. If all specified resources, e.g., tools,required for the selected workingstep are available, the decision makercommands the executor to perform the selected workingstep. Then, theexecutor accesses the tool-path DB and loads a corresponding tool-path.Thereafter, the executor converts the tool-path into a command forNCK/PLC and calls the adaptive control mechanism to set a variablecutting parameter.

Meanwhile, the operation is continuously monitored by the monitor. Incase a broken tool is detected, the monitor stops the operation anddrives an emergency handling mechanism. Concurrently, the monitorinforms the decision maker of the emergency. The decision maker checkswhether an available alternative tool exists in the machining resourceDB. If the alternative tool is found, the decision maker commands thetool-path generator to create a new tool-path for the remaining volume.The size of the alternative cutter may be different from that of theoriginal cutter. On the other hand, if no alternative tool is found inthe machining resource DB, the decision maker notifies the communicatorthat the corresponding workingstep cannot be conducted. Then, thecommunicator gives an alarm to the operator to request a new cutter. Inthe meanwhile, the decision maker attempts to find an alternativeprocess sequence according to the non-linear process plan. If thealternative process plan is found, the decision maker selects the nextworkingstep and directs the tool-path generator to generate a tool-path.

The tool-path generator inspects the validity of tool-paths in thetool-path DB and produces a new tool-path if required. If the nextworkingstep is concerned with measurement, the decision maker orders theinspector to perform a required process, i.e., to measure a target areaand store the measured data in the inspection DB. Then, the inspectorestimates a geometric error between the machining feature DB data andthe inspection DB data. If the estimated error goes beyond an allowableerror range, the inspector reports to the decision maker thatre-machining is demanded. In such a case, the decision maker adds a newworkingstep for the re-machining.

If one workingstep is completed, the decision maker updates the PSG ofthe machining process DB, the machine resource status information of themachining resource DB, and the machining knowledge DB according to theoperation result. Thereafter, the decision maker selects the nextworkingstep. This process is repeated until the all workingsteps arecompleted. Further, the decision maker directs the communicator to sendcurrent operational status information to the shop floor control systemwhenever the shop floor control system requests such information.

Referring to FIGS. 3A and 3B, there are provided a conceptual drawingand a block diagram, respectively for illustrating a development of theintelligent STEP-NC in accordance with the present invention.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. An intelligent STEP-NC comprising: a control module for reflectingfunctional level requirements of each controller of a machining tool; anSFP/TPG module for reflecting data interface level requirements; and acommon DB module for storing therein data generated, updated andreferred to by the control module and the SFP/TPG module, wherein thecontrol module includes: a decision maker for determining a sequence ofworkingsteps based on a diagnosis result, a monitoring result and aninspection result; an executor for converting a task sent from thedecision maker into a command, delivering the converted command to anNCK/PLC (Numerical Control Kernel/Programmable Logic Controller), andmemorizing the command performed by the NCK/PLC for an adaptive control;and a monitor for continuously monitoring the whole machine andmachining status, and transferring the monitored result as themonitoring result to an emergency handler or the decision maker, whereinthe emergency handler diagnoses an emergency when the emergency isreported from the monitor and, then, provides the diagnosed result asthe diagnosis result to the decision maker.
 2. An intelligent STEP-NCcomprising: a control module for reflecting functional levelrequirements of each controller of a machining tool; an SFP/TPG modulefor reflecting data interface level requirements; and a common DB modulefor storing therein data generated, updated and referred to by thecontrol module and the SFP/TPG module wherein the control moduleincludes: a setup manager for searching for a setup reference positionby moving a touch probe based on geometric information of a workpieceand a jig when the workpiece is placed on the machining tool; a decisionmaker for determining a sequence of workingsteps based on a diagnosisresult, a monitoring result and an inspection result provided from anemergency handler, a monitor and an inspector, respectively; an executorfor converting a task sent from the decision maker into a command,delivering the converted command to an NCK/PLC, and memorizing thecommand performed by the NCK/PLC for an adaptive control, wherein theNCK interprets a tool-path command among commands provided from theexecutor and operates a servo-mechanism to perform the tool-path commandwhile the PLC performs a machining tool command among commands providedfrom the executor; a monitor for continuously monitoring the wholemachining status by using a signal provided from a sensor, andtransferring the monitoring result to the emergency handler or thedecision maker, wherein the emergency handler diagnoses an emergencywhen the emergency is reported from the monitor and, then, provides thediagnosis result to the decision maker; an inspector for performing anin-process and a post-process inspection on the machining tool by usingan OMM (on-machine measurement) and delivering the inspection results tothe decision maker, a learner for analyzing the in-process inspectionresult received from the inspector and storing the analyzed data in thecommon DB module; and a communicator for interacting with externalunits.
 3. The STEP-NC of claim 2, wherein the executor brings theNCK/PLC a corresponding tool-path from the common DB module if the taskis concerned with a machining process but brings the NCK/PLC analternative tool from a tool magazine if the task is concerned with atool exchanging process.
 4. The STEP-NC of claim 2, wherein themachining tool command is concerned with, e.g., a tool exchange and aloading/unloading of a workpiece.
 5. The STEP-NC of claim 2, wherein theexternal units includes a CAD/CAM system, a shop-floor control systemand an operator.
 6. An intelligent STEP-NC comprising: a control modulefor reflecting functional level requirements of each controller of amachining tool; an SFP/TPG module for reflecting data interface levelrequirements; and a common DB module for storing therein data generated,updated and referred to by the control module and the SFP/TPG module,wherein the SFP/TPG module includes: an input manager for converting aCAD data inputted thereto into an internal geometric modeling kerneldata, recognizing a machining feature, extracting a property value ofthe machining feature and storing the extracted property value of themachining feature in the common DB module; a process planner forreceiving the property value of the machining feature from the inputmanager, determining a process sequence, a machining task, a jig, asetup and a cutter that are required for the manufacturing of themachining feature, and storing the determined data in the common DBmodule; a tool-path generator for generating a tool-path for machiningand measurement by using the determined data sent from the processplanner, and storing the generated tool-path in the common DB module;and a simulator for performing a cutting simulation before an actualmachining process in order to verify the generated tool-path and findpossible errors therein, and, then, storing the simulation result in thecommon DB module.
 7. The STEP-NC of claim 1, wherein the common DBmodule includes: a machining feature DB for storing machining featureinformation; a machine resource DB for storing information on astructure of a machine, available tools, a tool magazine, a jig and asensor; a machining process DB for storing a nonlinear process plan fora machining process which is expressed by using machining features,machining operations, a machining strategy, cutting parameters andcutting tools; a machining knowledge DB for machining knowledge byinteracting with an expert system; a tool-path DB for storing atool-path generated for a workingstep; and an inspection DB for storinga tool-path for a measurement and a result of the measurement.